Fabrication of Curie point written solid state magnetic memories

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Micropatterned amorphous films for thermomagnetic recording, TMR films using amorphous alloy layers, exchange biased films, and thermomagnetic recording process were investigated.(1) TbFe amorphous alloy films were prepared by rf magnetron sputtering, and microfabricated by focused ion beam (FIB) and conventional photolithography methods. Switching of the magnetization of TbFe elements was confirmed after current pulses which give rise to Joule heat in the elements. The current density necessary for the switching was found to decrease with decreasing the element size, and the 0.5μm squared element was found to be switched by applying the current density as small as 1.6 x 10^6 A/cm^2. In addition, tunnel junctions including TbFe amorphous alloy layer was found to exhibit sufficiently large magneto resistance ratio.(2) NiFe/Mnlr exchange biased films were microfabricated by FIB and their magnetic domain structures were observed by magnetic force microscopy (MFM). The easy direction of the NiFe/Mnlr elements lay in the film plane, and for such in-plane elements having 1 : 1 aspect ratio, it is difficult to obtain sigle domain state. Thus, the perpendicular magnetized elements such as TbFe were found to be effective to accomplish single domain state if the elements have 1 : 1 aspect ratio.(3) Simulation of thermomagnetic recording process was carried out, and the simulation was used to obtain material parameters which are necessary for recording of domains smaller than 100 nm. For the recording of domains smaller than 50 nm on an RE-rich TbFeCo medium, the increase of coercivity, which might be realized by controlling the microstructure of the TbFeCo film, was found to be needed.